The Mercedes-Benz CLS 350 CGI premiered with an innovative direct petrol injection recently. It was not until 1996 that gasoline direct injection (GDI) reappeared on the market. Mitsubishi Motors was the first with a GDI engine in Japan on its Galant range. Mitsubishi applied the technology widely, producing over 400,000 GDI engines in four families before 1999. The limiting factor, however was high sulphur content fuel, which led to emission problems and less than expected fuel efficiency. PSA Peugeot Citroen also launched a GDI engine with licensed Mitsubishi technology in 1999 but had to withdraw from the market in 2001. DaimlerChrsyler produced a special GDI engine in the year 2000 and offered it only in markets with low sulphur fuel. Following intensive development work, the company recently introduced the Mercedes Benz CLS 350 CGI with the world's first petrol engine with piezoelectric direct injection and spray-guided combustion. Yet another trend-setting technology from Mercedes-Benz, the piezoelectric direct injection and spray-guided combustion engine is claimed to achieve much better fuel efficiency and higher thermodynamic efficiency than conventional wall-guided direct injection systems. Forming the basis for future engine development work in this output class, the main advantage of the CGI engine (CGI = Stratified-Charged Gasoline Injection) lies in the stratified operating mode from which it takes its name. The most important components of this innovative direct petrol injection system are the fast-acting, high-precision piezoelectric injectors. It is on this invention and the way it has been translated into series-production technology that the most important advances associated with spray-guided combustion are based. The piezoelectric valves have injectors, which open outwards to create an annular gap just a few microns wide. This gap shapes the fuel jet and produces a uniform, hollow-cone-shaped spray pattern. The microsecond response times of the piezoelectric injectors provide the basis for delivering multiple injections per compression stroke, and thus for lean-burn operation. By allowing flexible and efficient control of the combustion process they play a key part in ensuring the engine's outstanding fuel efficiency. With the aid of simulations for the fuel mixture and the combustion process, the pistons have been designed with special piston bowl geometry, which concentrates the lean mixture in the area around the spark plug and prevents it from spreading out towards the cylinder wall. The piston shape therefore also plays its part in ensuring near-total combustion, low fuel consumption and low emissions in the direct-injection petrol engine. A high-pressure pump and downstream fuel rail and pressure control valve are responsible for delivering the fuel and regulating the quantity supplied. The peak fuel pressure in this system is up to 200 bar - around 50 times the fuel pressure in a conventional petrol injection system. DaimlerChrysler worked closely with Bosch, which is supplying the CGI injection system on the CLS. According to Dr Rolf Leonhard, Vice-President Development for Gasoline Systems at Bosch, "Gasoline direct injection with piezo injectors reduces consumption by up to 15 per cent compared with today's port fuel injection". Bosch claims that besides the piezo valves, the powerful engine management system is an important feature of the system. In 2005, researchers and developers from Bosch and Siemens VDO who worked independently on piezo technology for gasoline and diesel engines were jointly awarded the German President's "Zukunftspreis," the award for innovation and advanced technology. Bosch is now the first company to embark on mass production of a piezo-controlled gasoline injection system.Back to the CLS 350 CGI and the Mercedes-developed combustion process featuring multiple closely spaced injections on each compression stroke also results in smoother operation and improved emissions performance. Measurements, according to sources at DaimlerChrysler, show that engine-out hydrocarbon emissions in the warm-up phase are almost halved. Furthermore, since the injection and combustion processes can be actively controlled, it is also possible to raise temperatures in the exhaust manifold and thus speed catalytic converter warm-up. Just ten seconds after starting from cold, the direct-injection petrol engine reaches an exhaust temperature of over 700 degrees Celsius. Emissions are controlled by two close-coupled three-way catalytic converters with linear oxygen sensor control, which goes into operation immediately after the engine starts from cold. To reduce nitrogen oxide emissions, Mercedes-Benz has adopted a two-part strategy. This comprises, firstly, dual electrically controlled and cooled exhaust gas re-circulation which, depending on engine operating conditions, redirects up to 40 percent of the exhaust gases back into the cylinders. Secondly, it also comprises two underfloor NOx storage-type catalytic converters. Under lean operating conditions, these converters adsorb the nitrogen oxides. Periodically, during brief regeneration pulses, the nitrogen oxides are then desorbed, reacting with other exhaust gas constituents to form harmless nitrogen. Sensors upstream and down-stream of the catalytic converters monitor their operation. In addition, the new CGI engine also incorporates the same unique package of high-tech features as its conventional-injection counterpart. This includes four-valve cylinder heads, variable intake and exhaust camshaft timing, a two-stage in-take manifold, balancer shafts and intelligent thermal management with an electronically controlled thermostat. The crankcase and cylinder heads are of aluminium and the cylinder liners are of low-friction, thermally resistant, lightweight aluminium-silicon alloy. All fuel-carrying components of the CGI engine are of high-grade steel or brass; the rails in the area of the two cylinder banks and the housing of the high-pressure pump are of forged stainless steel. The new CLS 350 CGI is designed to operate on sulphur-free unleaded premium fuel and its state-of-the-art technology gives it the potential to adapt to emissions standards of the future. In Western Europe, the CLS direct petrol injection model will replace the current CLS 350. While the combination of direct injection with turbocharging is another avenue in the development of gasoline engines and enables greater revving range as well as development of higher torque in the lower speed range. For applications like the CGI engine of the CLS 350, Bosch has developed the second generation of the DI-Motronic, which, like the piezo system, delivers injection pressures up to 200 bar but keeps faith with solenoid-controlled injection valves. This will also be launched in 2006 - in a 1.6-litre engine jointly developed by BMW and PSA and destined for use in the Mini, among others. Leonhard sketches out the future market for gasoline direct injection: "We are assuming that by 2010, annual production of gasoline engines equipped with direct injection will top three million."